This specification relates to signal mapping, for instance to a receiver circuit for communication systems.
Communication systems can be used for information exchange between users. Such systems allow for data transmission over a wide range of distances and via different types of media (e.g., air and wire). Various coding techniques may be used to improve communication performance. Similar coding techniques may be used for storage systems.
FIG. 1 shows an example of a communication system 100 that includes a transmitter 110, a communication channel 120, and a receiver 130. The transmitter 110 receives an input (e.g., a digital bit string) and modulates it into a suitable form (e.g., an analog signal such as electromagnetic waves) for transmission over the communication channel 120 (e.g., air). The receiver 130 receives the transmitted signal and demodulates it back into the digital form for output.
In some applications, signals are coded prior to transmission for various purposes. One such application relates to error reduction and/or correction for signals delivered in the presence of channel noise. In these cases, an encoder 112 may be used to introduce carefully designed redundancy into the input signal to generate coded bit strings (sometimes also referred to as codewords). A mapper 114 establishes a direct mapping between the coded bit strings and a set of symbols, where each symbol corresponds to a respective value of a physical attribute(s) of the analog signal to be transmitted over the channel. At the receiver side, once the transmitted signal is received, a demapper 134 extracts bit estimates from the observed values, and a decoder 136 (or in some other examples, a soft iterative equalizer such as Viterbi equalizer) subsequently decodes the bit estimates to recover the digital signal.
As the received signals can be affected by channel noise, in some examples, it may be useful to first interpret the noisy signal as “soft” bits and then decode these soft bits into digital data. A soft bit provides a measure of reliability of bit estimates—in the case of binary coding, the probability of a received bit having a value of zero or one.